AKG K4/5xx familien:
Nedenstående er mere frit sammensat end tidligere indlæg i 'famileserien'. Der har været meget at konsumere kildemæssigt, og specielt i forhold til lydsignaturerne har jeg følt mig lidt på herrens mark (selv med min egen K500 at læse/tolke udfra). Det faktum at AKG løbende har lavet små og store ændringer (ofte uden officielt at indrømme det), gør ikke sagen enklere (ift lydsignaturer). Så, selv om diverse facts herunder er mere eller mindre korrekte (versioner, puder, mods, målinger mm), så må lydbeskrivelserne læses med forbehold. Der er i herværende indlæg links til kilder her og der, og i efterfølgende indlæg findes de fleste relevante billeder (fra samme links og andetsteds).
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AKG K400
Introduced 1991 alongside K500, both discontinued 1997. Probably 4 or more different revisions, though based on sound these are mostly narrowed down to Early Production (EP) vs Late Production (LP). The two are distinguisable by different headband, cable, jack plug, and driver (see below).
At least 3 different drivers have been identified, two of thesse in the EP version. This could account for the preference by some for one EP over another. Some seem to have a preference for EP over LP as well, the former being perceived as a bit more lively and musical, and the latter sounding warmer and lacking a bit of bass (comparably).
Generally the K400 seems to be perceived as musical and cohesive, slightly mid-focused, with tight rather than punchy bass, and with a good amount of PRaT, all making for a fun/enjoyable/intimate listen, rather than a critical/analytical one. Its character is said to be particularly well suited for things like chamber music, baroque ensembles, vocal music or small jazz formations.
Comparably..
K500 is said to be more neutral, detailed, dry, airy, cold
K501 is said to have less bass (quantity, not quality), more details (peakier), bigger soundstage, less speed/energy
K601 is said to be similar to K400, but fuller and slower (imore impact/presence, warmer/darker, less airy, smaller soundstage)
K400 versions
EP: Headband rubber/vinyl/plastic. Plug all golden. Cable thinner. Driver A & B
MP: Headband leather. Plug all golden or partly black. Cabler thinner. Driver B
LP: Headband leather. Plug partly black plastic. Cable thicker. Driver C
Driver A: Large driver hole with foam. This foam will likely have deteriorated, and should be changed to new foam (or tape with a small hole, or micropore - it's possible to tune the bass here in many ways). Twelve filtered openings. Driver connections close together on the same side, with a blue glue blob to fix one of the wires to the diaphragm (which can cause an annoying rattle). All metal plug.
Driver B: Large driver hole but with rubber grommet to make it smaller (grommet can be removed with a pair of pliers and some force). Four filtered openings. Driver connections close together on the same side, with a blue glue blob to fix one of the wires to the diaphragm (which can cause an annoying rattle). All metal plug.
Driver C: Small driver hole. Four filtered openings. Driver connections on opposite sides of the driver (like later K701). No blue glue. Metal/plastic plug and leather headband.
Same baffle on all three, though some (LP?) versions in addition have a removable treble filter.
If you take off the pads and hold the headphone in strong light you can easily see if it has four or twelve filtered openings, and if it's a grommet/small hole version. If the centre of the driver is dark it's most likely the foam version, which probably needs to have its foam changed.
Examples/pictures can be found here and here, and some of the same pictures can be found below.
K400 mods
Pads: There seems to be a general preference for K400 with original K400 pads, but K601 pads are a runner up with their added body and weight to the sound, while retaining the hailed mids of K400. (example)
Driver/Baffle: Some choose to mod the K400 baffle, mimicking K501 baffle versions 1 & 3.
Cable: EP and LP have different wiring inside the cup, only LP is shown in the service manual, so this link shows the EP wiring (also see pictures below). If already in there it might also be worth cleaning the steel contact rods, as well as check/correct for phase problems (cf this link).
Balanced: Both K400 and K500 are said benefit from rewiring to balanced, resulting in increased clarity and resolution, K400 reacting the most to this mod.
https://www.head-fi.org/threads/akg-k400.15013/
AKG K500
The AKG K500 is the more expensive bigger brother of the K400 with more luxurious looks and headband as well as a different colour scheme.
There appears to be silmilarities in revisional changes/improvements for K400 and K500. At a fundamental level 3 different drivers have been identified for K500, and all are said to sound quite different. Pads, cords and plugs also vary, but the driver differences are the deciding factor when determining production period..
Driver A (EP): Half matte diaphragm and 12 openings at the back of the driver (dampened with white fibre paper). Removable treble filter on some, others without. All metal plug and adapter, and somewhat thicker cable.
Driver B (MP): Most common version. Half matte diaphragm but only 2 + 2 holes at the back of the driver. On the diaphragm two types of ridges combined (short ridges at the rim, longer ones at the centre). All metal plug and adapter.
Driver C (LP): 2 + 2 holes at the back of the driver, but a clear diaphragm with a simplified ridge pattern (only long, single ones). Same cable as MP, later a partly black plastic plug with metal adapter and slightly thinner cord (as on the K401 and K501).
Same baffle on all three, though some EP versions in addition have a removable treble filter.
Ear pads
The original grey K500 ear pads are no longer available. There were also different versions of these, where the rim ring isolation foam/soft plastic (on some non-existant) between pad and baffle seemed to influence the "tightness" of sound.
Condition of the pads affect the response as well. If not completely destroyed, it is worth trying to rescue the original ones by cleaning in mild soap water and massaging back into shape.
K501/400, K601 and K701 pads are still available (e.g. from Thomann), if the original ones are destroyed, or if a different tuning is desired..
K501 pads are said to tighten up the sound overall (cleaner, more controlled)
K601 pads (velour) are said to add sligthly more body to the bass, otherwise retaining the sonic character
K701 pads (velour) are said to tame the highs, though also take away from the liquid mids
K702 pads (angled) are said to basically increase everything (sounding somewhat unnatural)
Mods / repairs
Foam damper/baffle filter: Tuning the foam damper (often totally disintegrated) in the hole on the back of the driver and covering some of the paper slits on the baffle results in a more balanced response, with fuller bass and less strident treble (soundstage is unaffected).
Presence/Treble filter: Early K500 baffle had a removable filter cap (as did early K400).
Connection problem: Internally, the two cables are clipped onto the driver, and the connectors tend to loosen over time. Just open the cup, tighten the metal connectors, clip them on again, and put things back together. (cf K400 link).
Plug adapter: If the 1/4" adapter for the all golden plug (K500 EP/MP) is lost, Thomann has an Audio-Technica 1/4" adapter that will fit. The adapter from the plastic/metal plug (K500 LP) will not fit the all golden plug.
Amping
There is no consensus. Some call it harder to drive than K701 and on par with K340. Others put it just above K601 in terms of amplfier requirements. Some say it needs sufficient voltage swing to shine, others say it needs suffient current as well. Underfed it said to lack bottom end impact.
Measurements show both K500 and K501 to have considerable lows roll-off. Some will perceive this as realistic and tight bass, others will mind the lack of low extension
Here a valve amp can give the 'illusion' of fuller bass. It doesn't have more bass in quantity, but appears fuller (more prominent) as more harmonics are 'generated' that give bass it's 'feisty feeling'.
Sound comparisons
K500 sounds similar to K400, but with more refined treble. Bass and mids sound identical to K400, with the same shortcoming (lack of body and bass extension). Tonal balance is ‘accurate’ and very realistic, with a bright ‘edge’ resulting in a slight feeling of ‘extra detail’.
K400: Warmer, more cohesive, more musical, better all-rounder, works with many different genres
K500: Brighter, more neutral, better detail/clarity and treble extension, can sound clinical
K500: Less bass (even with K601 pads), cleaner and more transparent, bigger soundstage
K501: More midrange body (and smoother as well), upper midrange glare,
Both: Very large soundstage (bigger than K701), good instrument separation (not as good as K701), able to maintain intimacy (enough forwardness in upper midrange),
https://www.head-fi.org/threads/akg-k500-love.562787/
AKG K401
K401 and K501 were both introduced 1996, replacing K400 and K500. They made use of the new, patented Varimotion (two-layer) diaphragm, which later also was used in K601 and K701 (in different incarnations). The sonic kinship between the two is said to be closer than that between their predecessors, with both leaning more towards K500 than K400.
Compared to K501 the smaller brother is said to have slightly more bass impact (though a little bloated) with less refined/euphonic upper-mids/highs and some etchiness to the highs. These are nuances, both are still said to have a balanced/natural yet analytical sound, with light/tight bass and large soundstage.
Impressions/reviews are somewhat scarce compared to the other K4/5xx models, and it's unclear if K401 underwent different revisions during its lifespan. It was discontinued 2003, while production of K501 continued until 2006, when K601 and K701 were introduced.
AKG K501
The successor of K500, with the familiar AKG look but a different color-scheme, and with the new Varimotion driver.
Efficiency is not very high, and with not enough voltage swing K501 will sound ‘raw’ and compressed at louder volume levels. Amplifier output resistance (low-Z vs high-Z) has little effect on tonal balance/frequency response, though.
K501 shares the rolled of bass with its predecessor. Some hear this as lean or anaemic, to others it sounds tight and right. Combined with different versions, pads, amps, and preferences, this makes for quite varied perceptions and descriptions of K501. Hence the two attempts below to capture the sonic character.
View A:
K501 has a nicely rendered, coherent and well-integrated midrange. Virtually flat from 80-4000 and with a slight dip in the sibilant area of 4000-6000, followed by a slight boost from 6000-8000 and a gentle roll off until about 11,000. A fairly high THD (relative to some on the market) might account for a bit of added "warmth" overall.
K501 bass is great for acoustic music when properly amped. It will not do an electric bass or electronica well, but piano, low brass and woodwinds, standing bass, and other non-amplified instruments sound perfect.
In classical and acoustic jazz music it renders higher harmonics from the strings, brass and woodwind instruments naturally and accurately. In vocal music it gives a credible perception sense of living, breathing vocals. Acoustic and vocals is where the K501 does best, genres that don't require (as much) lower mids and bass.
Great all-around sound, an overall coherence makes listening so involving and complete.
View B:
K501 is all about the mids, which have almost too much clarity, and can sound too forward and shouty on a lot of music. Treble is also accentuated and with a bit of sibilance and sharpness to it, can sound ‘raspy’ and lacks ‘air’. Bass is rolled-of considerably (lacks body and extension, like K500), and therefore will sound ‘tight’ but ‘thin’. Bass does integrate well into mids, however, and therefore does sound realistic (albeit thin).
Even if clarity is K501’s particular forte, it can still be a bit much for some. Different pads or port sealing can remedy this to some extend. The black K702/712 velour pads will make K501 sound a bit warmer and less forward, and with less clarity (maybe even slightly lacking). For a finer clarity/treble tuning one or more ports around the driver can be sealed (with tape, thus reversible), bass is unaffected by this mod.
Versions
There are 3 different versions. The driver is the same, but the baffle is different. V1 share baffle with K401, V2 share with K400/K500, V3 share with K601/K701. In terms of production period the order therefore should read V2 (early), V1 (mid), and V3 (late).
Version 1: [3/6 + 4/12 + black] - baffle has 3 long openings out of a possible 6, and on the next level 4 smaller openings out of a possible 12, with a black dampening covering them.
Version 2: [6/6 + 12/12 + white] - baffle has 6 long openings and 12 smaller ones, with a white dampening material which is thick.
Version 3: [6/6 + 0/12 + white] - baffle has 6 long openings with no smaller ones, with a white dampening material as well, but is thinner and more porous than Ver.2.
Pads also vary between versions, they are similar between V1 and V3, but are a less shiny black and have yellow/orange foam on V2.
Some V3 pads are claimed to have more bass, these have a brown sealing ring at the back (silicone-like), rather than black (foam). Could be different foam density in pads themselves, and not the sealing ring, that is responsible, it is not clear. AKG have stated that no changes were made to the pads.
V2 is said to have the least bass (due to all ports open), V3 the most (partly due to pads). The two are sometimes refered to as the K501 Bass-ligth and K501 Bass-heavy versions.
The effect of different dampening material (black/white) is said to be neglible, V2 can sound like both V1 and V3 just by blocking up the different holes/ports.
https://www.headfonia.com/akg-k500-k501/2/
https://diyaudioheaven.wordpress.com/he ... /akg/k501/
Service Manual